Beamshaper for optical head

ABSTRACT

An optical head of a type useable in a optical disk reader/writer is provided. One of the optical elements is provided in a fashion that one or more optical parameters or characteristics of the system are invariant, regardless of whether the one optical element is used, or not. In one embodiment the optical element is a beamshaper. In order to provide the desired invariant property, the surfaces of the optical element are preferably formed with high accuracy. One manner of economically achieving high accuracy is to measure errors or imperfections in a first formed, preferably etched, surface and adjust the shape or position of a second aligned etched surface so as to at least partially compensate for the errors or imperfections.

The present application is a continuation-in-part of U.S. applicationSer. No. 09/540,657, filed Mar. 31, 2000 which is a continuation-in-partof patent application Ser. No. 09/457,104 filed Dec. 7, 1999, bothincorporated herein by reference. Cross reference is made to U.S. patentapplication Ser. No. 09/315,398 entitled Removable Optical StorageDevice and System, filed May 20, 1999, and to U.S. patent applicationSer. No. 09/527,982 filed Mar. 17, 2000 which claims priority in U.S.Patent Application No. 60/140,633 entitled Combination Mastered andWriteable Medium and Use in Electronic Book Internet Appliance, filedJun. 23, 1999, all incorporated herein by reference.

The present invention is related to an optical head, e.g., for use inreading from and writing to an optical disk and in particular to anoptical head wherein a beamshaper may be provided without substantiallychanging a virtual beam source point, or one or more other opticalparameters.

BACKGROUND INFORMATION

Optical read/write devices, as with many complex optical devices,commonly include a plurality of different optical elements along anoptical path which can affect characteristics of the beam which travelsalong the optical path. For example, depending on the design andconfiguration of the device, the optical path may include one or morelenses or other refractive elements, holograms, gratings or otherdiffractive elements, flat or shaped mirrors and the like. Each elementin an optical path can change one or more optical characteristics of thebeam and/or may influence the manner in which other, “downstream”optical elements influence the beam. The resultant multiple opticalcharacteristics and interactions of the various elements often resultsin a optical system which is difficult, time-consuming and expensive todesign, test, fabricate and the like. For this reason, creating multipledifferent optical path designs, or making modifications in an opticalpath design is not done lightly or easily, especially for complexoptical devices such as an optical read/write device.

In addition to the cost of designing complex systems, there are alsocosts associated with maintaining stocks or inventories of componentsneeded to fabricate two or more different systems, costs associated withdesigning devices and/or training personnel for assembling two or moredifferent devices, maintaining or repairing two or more differentsystems and the like.

Previous approaches to optical read/write devices have typicallyinvolved a choice between either foregoing the anticipated or potentialadvantages that might arise from a new or modified design (in order toavoid certain costs), or undertaking the costs associated with a new ormodified design in hopes that the costs for the new or modified designwill be justified by technical, marketing, manufacturing or otheradvantages arising from the new or modified design. Unfortunately,because of the complexity of optics in general and interactions betweenoptical components, it is often infeasible to accurately determine thecost for a new or modified design, or the advantages associated with aproposed new or modified design, in advance. Accordingly, it would beuseful to provide a method, system and apparatus which can provide forone or more changes in the optical design, such as adding or changing afirst element along an optical path of a read/write device (or otheroptical device) while reducing or substantially eliminating the changesin at least some optical parameters or characteristics of other opticalelements in the optical path (or how such other elements affect thebeam). By reducing or eliminating influences on, or changes in operationof other optical elements (for at least some optical parameters) it ispossible to reduce or avoid the need for redesigning other opticalelements in the system, as a consequence of changing, adding orredesigning one (or a group) of optical elements, and thus reducing theoverall cost associated with a design change or modification. Byreducing the cost of system design change or modification, as well as byreducing the uncertainty in estimating the cost (since a smaller numberof components need to be changed, modified or added) it becomes morefeasible to develop multiple or modified optical path designs which canbe useful both during product or system development (e.g., permittingparallel development of two or more different options for a design)and/or for accommodating two or more different potential componentvendors, sources, component characteristics and the like.

In one situation, it may be desirable to perform parallel development ona design which includes a beamshaper and second design which does notinclude a beamshaper. For example, in a system which provides laser (orother) light to an objective lens (as described below) for addressing anoptical disk or similar medium, it may be possible to achieve a desiredlight intensity profile at the objective lens by “overfilling” the lens(and “spilling” the relatively lower-intensity light at the perimeter ofthe beam). On the other hand, this technique can result in spilling orwasting a substantial amount of the total laser (or other light source)output, requiring a higher-power source in order to achieve desiredintensity (or intensity profile) as delivered to the medium.Higher-power laser devices or other sources may be not only moreexpensive but may lead to certain secondary costs or effects such ascosts of a larger power supply and/or a need for dissipating a greateramount of heat. Accordingly, it may be useful to include a beamshaperwhich can assist in delivering the desired intensity (or intensityprofile) to an objective lens, without the need for overfilling thelens, e.g., by “circularizing” or otherwise changing the beamcross-sectional shape and/or by changing the beam (cross-sectional)intensity profile. In many situations, it may be infeasible to know, inadvance, which option is preferable. However, it may be economicallyinfeasible to create two or more completely different optical pathdesigns (i.e., modifying all or substantially all optical elements inthe optical path), especially given the complex interaction betweenoptical components, even though only one of the designs is likely to beultimately used. Accordingly, it would be useful to provide a method,system or apparatus for an optical read/write device (or other opticaldevice) in which the operation or nature of a plurality of elementsalong the path, and/or the magnitude or nature of at least some opticalparameters of the beam, is substantially unchanged regardless of whetherthe optical path includes a beamshaper or does not include beamshaper.In this way it would be possible to, e.g., design an optical path whichdid not include a beamshaper, and yet have the ability to insert abeamshaper, if that option is ultimately desired, while reducing oreliminating the need for redesigning other (non-beamshaper) elements oraspects of the optical path.

The usefulness and/or need for a beamshaper in an optical path of thetype described above can be, at least in part, dependent on thecharacteristics of the laser or light source. Not uncommonly, batches oflasers, as delivered, may have a substantial amount of variability inthe characteristics of the output light. Thus, in a manufacturingcontext, even within a single batch or delivery of laser devices, theremay be some which operate best in a system without a beamshaper andothers which operate best with (or require the use of) a beamshaper. Inprevious approaches, typically it was necessary to either undertake thecosts of completely designing or modifying the optical path, to producetwo completely different designs (i.e., changing or modifying all orsubstantially all components in the optical path), one for use withlasers that require a beamshaper, and another for use with remaininglasers, or to select one of the designs with the knowledge that a numberof lasers (or other light sources) in any order or batch will need to bediscarded or otherwise disposed of. Accordingly, it would be useful toprovide an optical system which is substantially the same in all ornearly all non-beamshaper components, regardless of whether a beamshaperis present, or not. In this way, it is feasible to use substantially alllasers (or other light sources) in an order or batch, but withoutincurring costs needed for developing two completely different opticalpaths.

A number of optical reader/writer devices, including, for example,relatively large devices such as audio compact disk (CD) players in atypical home stereo system, present relatively little concern with powermanagement or power budgets (typically having access to AC line levelpower or the like). As a result, in many such systems, it is feasible toprovide an optical design which is relatively inefficient of opticalpower (such as by substantially overfilling lenses and the like, e.g. toaccommodate noncircularity of laser sources). In contrast, devices suchas those described in application Ser. No. 09/315,398, supra and or60/140,633 intended to be lightweight and portable, generally mustoperate with a limited power budget (and also have a more limitedability to dissipate heat, compared with larger systems). Accordingly,it would be useful to provide an optical head apparatus, system andmethod which can achieve the desired optical quality (e.g. accommodatingnoncircularity or other optical features) while avoiding, as needed oruseful, undue energy inefficiency and/or unnecessary heat generation(e.g. arising from substantial overfilling of lenses or other opticalinefficiencies which in turn require higher optical power and hencehigher electrical power lasers which dissipate more heat).

SUMMARY OF THE INVENTION

The present invention includes a recognition of problems in previousapproaches, including as described herein. According to one aspect ofthe invention, an optical element unit (OEU) which includes at least afirst non-beamshaper element of an optical path, can be provided withone or more beamshaper elements, also positioned on the optical elementunit, and also being in or part of the optical path. The beamshaper isconfigured in such a manner that at least some optical characteristicsof the beam are substantially unchanged regardless of whether thebeamshaper is provided or not. In one embodiment, the virtual sourcepoint for a laser diode light source is substantially the sameregardless of whether the beamshaper is present or not. In oneembodiment, although the presence or absence of the beamshaper has anaffect on the optical properties of the beam, it is not necessary (inorder to provide a feasible and operable read/write device) tosubstantially alter any of the non-beamshaper components on the opticalpath, to accommodate the addition of a beamshaper. In this way, it ispossible to substantially design the entire optical path for aread/write device in the absence of a beamshaper and, if it is laterdetermined that a beamshaper is desired or necessary, to insert thebeamshaper component or components into the optical path without theneed for substantially altering or modifying or adding other componentsalong the optical path.

In one embodiment, in order for a beamshaper to have thischaracteristic, the lens or other surfaces of the beamshaper must befabricated with a degree of accuracy, e.g., within a few percent ofideal position or shape. In many previous approaches, the cost ofproviding such accuracy would substantially outweigh the benefits ofproviding a beamshaper of this nature. However, according to oneembodiment of the invention, it is possible to achieve a beamshaper witha high degree of accuracy while maintaining cost-feasibility. In oneembodiment, one or more beamshaper surfaces are formed by a photomaskand etching process. Examples of operable photomask and etchingprocesses are described in U.S. patent application Ser. No. 09/666,616,filed Sep. 20, 2000, and titled “Microlens and Method and Apparatus forFabricating” incorporated herein by reference. For example, a suitableshape can be formed by etching a fused silica substrate using agray-scale mask, or multiple masks. Such etching processes can achieve ahigh degree of accuracy in a surface shape, at relatively low costs(e.g., compared with grinding, molding or other lens formationprocedures).

Cost-feasibility can be further provided by forming at least one surfaceof the beamshaper simultaneously with forming a second (e.g.,non-beamshaper) optical element on the same block (e.g., an “opticalelement unit” or OEU as described below). Simultaneous etching of two ormore components reduces per-element formation time and cost requirementsand can result in highly accurate lateral placement of two or moreelements relative to one another, further reducing costs (e.g., ascompared with providing discrete elements which must be separatelypositioned).

Additional cost-feasibility can be provided by using a wafer-scaletechnology in which multiple OEUs are etched in a single large (e.g., 6inch diameter) wafer, with the OEUs being subsequently separated fromone another by sawing or the like.

Another manner of providing highly-accurate beamshaper shapes, whilemaintaining feasible costs, is to shape or form two (or more) lenssurfaces of the beamshaper in non-simultaneous (e.g., sequential) stepsor stages, thus making it possible to measure shapes, positions,features or imperfections in a first beamshaper surface, and adjust theshape of the second beamshaper surface to at least partially compensatefor errors, imperfections or tolerances in the first beamshaper surface.In one embodiment, after a first surface of an OEU is formed to includea first beamshaper surface, the shape, position or other opticalparameters or features of the first beamshaper lens surface aremeasured. In a later step or stage, a different (e.g., opposite) surfaceof the OEU is etched and the etching process is performed in such amanner as to etch the second surface to at least partially compensatefor errors or imperfections in the first surface (e.g., by designing orselecting a photo mask for the second surface, and or adjusting etchtimes or other parameters to achieve the desired compensating secondbeamshaper surface). Of course, there may be errors or imperfections inthe etching of the second surface. However, by providing measurement andcompensation as described, it is more likely that the respective errorsin first and second beamshaper surfaces will be at least partiallysubtractive in nature, rather than additive in nature. I.e., in theabsence of the described measurement and compensation procedure, a 3%shape or position error in each of the two surfaces could be additiveand result in an overall beamshaper error of about 6% or more. By usingthe described measurement and compensation process, the likelihood isthat if there is a 3% error in shape or position for each matchingprocess, errors in the first process will be substantially nullified,resulting in an overall beamshaper error of about 3%.

In one aspect, an optical head of a type useable in a optical diskreader/writer is provided. One of the optical elements is provided in afashion that one or more optical parameters or characteristics of thesystem are invariant, regardless of whether the one optical element isused, or not. In one embodiment the optical element is a beamshaper. Inorder to provide the desired invariant property, the surfaces of theoptical element are preferably formed with high accuracy. One manner ofeconomically achieving high accuracy is to measure errors orimperfections in a first formed, preferably etched, surface and adjustthe shape or position of a second aligned etched surface so as to atleast partially compensate for the errors or imperfections.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a reader/writer drive devicecoupled to a host device of a type that can be used in connection withembodiments of the present invention;

FIG. 2 is a perspective schematic view of an optical arm and opticaldisk according to an embodiment of the present invention;

FIG. 3 is a perspective view of an optical head according to anembodiment of the present invention;

FIG. 4 is a top plan view of the optical head of FIG. 3.

FIG. 5 is a side elevational view of an optical head of FIG. 3;

FIG. 6 is a cross sectional view through an optical head and a portionof an adjacent disk according to an embodiment of the present invention;

FIG. 7 is a perspective view partially exploded of a wafer and partiallymounted spacer components according to an embodiment of the presentinvention;

FIG. 8 is a top plan view of a portion of a wafer with mounted spacercomponents;

FIG. 9 is a top plan view of one resultant wafer section following wafercutting;

FIG. 10 is a vertical cross section through an optical head and aportion of an optical disk according one embodiment of the presentinvention;

FIG. 11 is a partial perspective view depicting an optical arm and arelatively movable optics head, according to an embodiment of thepresent invention;

FIG. 12 is a partial exploded perspective view of an optics arm andoptics head according to an embodiment of the present invention;

FIG. 13 is a partial perspective view of a portion of an optical armwith mounting prongs, according to an embodiment of the presentinvention;

FIG. 14 is a vertical cross sectional view of an optical head accordingto an embodiment of the present invention;

FIG. 15 is a side elevational view of components of an optical head witha laser mounted on a surface of the optical die, according to anembodiment of the present invention;

FIG. 16 is a side elevational view of components of an optical headwhich uses a VCSEL, according to an embodiment of the present invention;

FIG. 17 is a block diagram depicting components that can be uses inproviding various embodiments of the present invention;

FIG. 18 is a longitudinal cross sectional view of an optical headaccording to an embodiment of the present invention;

FIG. 19 is a top plan view of an Optical Element Unit (OEU) according toan embodiment of the present invention;

FIG. 20 is a bottom plan view of an Optical element unit according to anembodiment of the present invention;

FIG. 21 is a transverse cross-sectional plan view of an Optical elementunit (OEU) according to an embodiment of the present invention;

FIG. 22 is a top plan view of an optical detector portion of an opticalhead substrate, according to an embodiment of the present invention;

FIG. 23 is a side elevational view of the portion of the substrate ofFIG. 22 combined with a corresponding portion of an Optical element unit(OEU), with selected light beams shown cross-hatched, for clarity,according to an embodiment of the present invention;

FIGS. 24A and B are graphs of Focus Error Signals (FES), as a functionof focus at the medium, for first and second detectors, respectively,according to an embodiment of the present invention;

FIG. 25 is a graph of a differential Focus Error Signals (FES), as afunction of focus at the medium, according to an embodiment of thepresent invention;

FIG. 26 is a side elevational view of an optical head, with arrowsshowing the paths of central axes of selected light beams, according toan embodiment of the present invention; and

FIG. 27 is a side elevational view of an optical head, with arrowsshowing the paths of selected light beams, according to an embodiment ofthe present invention.

FIGS. 28A and 28B are schematic depictions of invariant virtual sourcepoints in optical paths, without and with (respectively) a beamshaperaccording to an embodiment of the present invention;

FIG. 29 is a flow chart illustrating a fabrication process according toan embodiment of the present invention;

FIGS. 30A and B illustrate the Y and X sag profiles for the first lenssurface of Equation (1) and Table I, according to an embodiment of thepresent invention;

FIGS. 31A and B illustrate the Y and X sag profiles for the second lenssurface of Equation (1) and Table I, and according to an embodiment ofthe present invention; and

FIG. 32 illustrates an example of changing refraction at a second lenssurface to compensate for error in refraction at a first lens surface,according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention can be used in the context of a number of drivesand drive configurations, including as described in U.S. patentapplication Ser. No. 09/315,398, supra. In the configuration depicted inFIG. 1 a reader/writer drive device 112 is coupled to a host device 114(which may be, for example, a personal electronic device (PED) such as amusic and/or video player, a camera, and electronic book or other textreader and the like) by an interface 116. In the embodiment depicted inFIG. 1, the drive 112 holds or receives optical media, typically anoptical disk 118 which has a hub 122 for coupling or centering withrespect to a disk spin motor 124 under control of a motor control 126.In one embodiment, the media 118 is a first surface media, e.g. asdescribed in U.S. patent application Ser. No. 09/315,398 supra.,incorporated herein by reference. Bits on the media 118 are read orwritten using an optical head 128 (e.g. as described more thoroughlybelow) which provides data or signals 132 to a data read/writeelectronics 134, e.g., for passing to the host 114 via the interface116. The optical head 128, in one embodiment, includes substantially allcomponents or devices which control or affect the laser or optical beamalong its entire path from generation to arrival and/or reflection fromthe media 118 and detection, including the laser or other light source,lenses, gratings, holograms, wave plates, mirrors, beam splitters andother refractive, reflective, diffractive or other optics for affectingthe light beam or controlling photo diode or other light detectors andthe like.

Before discussing details of the present invention, certain generalconcepts will be discussed. One of the important factors affectingdesign of an optical system (such as a system for an optical diskreader/writer, typically including a laser or other optical source,lenses, reflectors and other components) is the size of the opticalsystem, both in terms of the mass, volume and/or dimensions and in termsof the size and shape of the light as it reaches the optical disk (thespot size and quality). Although a wide variety of systems have beenused or proposed, typical previous systems have used optical componentsthat were sufficiently large and/or massive that functions such as focusand/or tracking were performed by moving only some components of thesystem, such as moving the objective lens (e.g. for focus) relative tothe laser or other light source. Without wishing to be bound by anytheory, it is believed that the relatively large size of components wasrelated to the spot size, which in turn was substantially dictated bydesigns in which the data layer of a disk was significantly spaced fromthe physical surface of the disk (so that the optical path typicallypassed through a disk substrate, or some other portion of the disk,typically passing through a substantial distance of the disk thickness,such as about 0.6 mm or more, before reaching the data layer).

Regardless of the cause behind providing for relative movement betweenoptical components, such an approach, while perhaps useful foraccommodating relatively larger or massive components, presents certaindisadvantages, including the relatively large form factors required andthe cost associated with establishing and maintaining optical alignmentbetween components which must be made moveable with respect to oneanother. Such alignment often involves manual and/or individualalignment or adjustment procedures which can undesirably increasemanufacturing or fabrication costs for a reader/writer, as well ascontributing to costs of design, maintenance, repair and the like.Accordingly, an optical head method, system and apparatus which canreduce or eliminate the need for relative movement between opticalcomponents, during normal operation and/or can reduce or eliminate atleast some alignment procedures, e.g., during reader/writermanufacturing, can be useful.

Many early optical disks and other optical storage systems providedrelatively large-format reader/writer devices including, for example,devices for use in connection with 12 inch (or larger) diameter disks.As optical storage technologies have developed, however, there has beenan increasing attention to providing feasible and practical systemswhich are of relatively smaller size. For some applications, e.g., foruse in personal electronic devices (PEDs), e.g. as described in U.S.patent application Ser. No. 09/315,398 for Removable Optical StorageDevice and System (incorporated herein by reference), a device forreading and/or writing optical disks is described having a relativelysmall form factor such as about 10.5 mm height, 50 mm width and 40 mmdepth. Generally, a practical reader/writer device must accommodatenumerous items within its form factor including the media, mediacartridge (if any), media spin motor, power supply and/or conditioning,signal processing, focus, tracking or other servo electronics, inaddition to the components associated or affecting the laser or lightbeam optics. In order to facilitate a relatively small form-factor, anoptical head apparatus, system and method which can occupy a relativelysmall volume can be useful. In addition to total volume considerations,constraints imposed by a desired form factor and/or the need toaccommodate other reader/writer components can make it advantageous toprovide an optical head apparatus system and method which is relativelysmall in certain dimensions such as having a relatively small verticalprofile or dimensional requirement (with “vertical” referring to adirection parallel to the optical disk spin axis), although reduction ofrequirements in other dimensions (such as a longitudinal dimensionparallel to an optical arm axis and/or a lateral dimension perpendicularto the longitudinal axis) may also be of importance. Provision of a lowvertical profile configuration can be specially problematic since, forat least some optical designs (including, e.g. finite conjugatedesigns), a minimum optical path may be required or advisable (althoughthe read/write beam generally must reach the optical disk substantiallynormal to the plane of the disk). An optical head apparatus system andmethod which can reduce dimensional requirements such as reducingvertical dimension requirements, e.g., in the case of a PED to less thanabout 12 mm, preferably less than about 5 mm and more preferably lessthan about 3 mm, can be useful.

Preferably, some or all electronics for controlling and/or modulatingthe laser and/or conditioning, digitizing and/or processing detectionsignals are included in the optical head. Information or signalsobtained using the optical head 128 are also provided 136 to an armcontrol electronics 138 which moves or controls an optical arm 142, e.g.for tracking and/or focus. A power source or conditioner 144 providespower for electronics and/or motors or actuators. Various configurationsof a drive 112 can have other components, not depicted in FIG. 1, suchas mechanical components for receiving and/or ejecting the media 118and/or media cartridges, content control electronics, microprocessors orother processors, data storage memory devices, dataencryption/decryption electronics, and/or other components as will beunderstood by those of skill in the art after understanding the presentdisclosure.

The size, mass, volume, shape and/or vertical, longitudinal and/orlateral dimensions or requirements and/or cost of the optical head 128are of significance to the overall feasibility and cost of a drivedevice 112, especially when the configuration of the drive device 112places constraints on the position, size, shape or cost of othercomponents of the drive 112, and particularly when it is desired tosubstantially accommodate the drive 112 in a certain form factor, e.g.,as described in U.S. patent application Ser. No. 09/315,398, supra.

FIG. 2 illustrates in generalized or schematic form, a positionalrelationship of an optical head 128 and arm 142 with respect to media118 according to one embodiment of the present invention. In theembodiment of FIG. 2, the optical head 128 is mounted in a fixedposition with respect to the optical arm 142. As described morethoroughly below, preferably, all components of the optical head 128 arein a constant or fixed position with respect to one another, i.e. thereis substantially no relative movement of any optical component of theoptical head 128 with respect to any other component of the opticalhead. Instead, in the depicted embodiment, to achieve desired alignmentwith data on the media 118 (i.e. tracking) and/or focus, the entireoptical head 128 is moved, as a unit, with respect to the media 118.

In a preferred embodiment, the optical path is configured such that theoptical path length (measured along the optical axis, following anyfolding of the optical path) from the source to the objective issubstantially greater than the distance from the objective to the datasurface of the medium. In one embodiment, the ratio of thesource-to-objective path length to the objective-to-data surface pathlength is at least about 5. As used herein “objective” or “objectivelens” refers to the component which focuses light onto the recordinglayer or recording surface of the medium. Although this is typically aconventional refractive lens, it can also include reflective,diffractive, or holographic components . Although typically the last orultimate optical component along the optical path before the lightreaches the medium, “objective” or “objective lens” as used herein canalso encompass items which may not be the last optical component beforereaching the medium. The optical path length from the objective to thedata surface is a function of a number of factors including thenumerical aperture of the lens, the distance (if any) from the disksurface to the data surface and the smallest safe spacing between theoptical head and the disk surface (the “working distance”). In oneembodiment, it is desired to provide an optical path length from thesource to the objective greater than about 2.5 mm, preferably greaterthan about 4 mm, and even more preferably greater than about 4.5 mm. Oneembodiment of the present invention involves achieving such asource-to-objective path length while providing a low-profile device,preferably such that a reader/writer device can be accommodated in aform factor with a (vertical) profile less than about 10.5 mm,preferably less than or equal to about 6 mm.

In the depicted embodiment, media 118 rotates 212 about a spin axis 214which defines what will be referred to herein as the vertical direction.Spinning of the disk 212 provides for alignment of the light beam with(successive) circumferential positions on the disk 118. Alignment withdesired radial positions (tracking) is provided by moving the opticalhead 128 in a direction having a radial component, preferably byrotating 216 the optical arm 142 about a substantially vertical axis 218so that the position at which the light beam reaches the disk 118defines an arc 222 extending throughout a predetermined radial range ofthe disk 118. In the depicted embodiment, to provide focusing, theentire optical head 128 is moved, as a unit, along a path having avertical component such as by pivoting 224 the arm 142 about asubstantially horizontal axis 226. Although the illustration of FIG. 2is not to scale, it suffices to illustrate that the overall verticaldimension for accommodating the component depicted in FIG. 2 will beaffected by the vertical profile or height 232 of the optical head 128,as well as other dimensions such as the spacing 234 to the media 118 andthe like.

FIG. 2 depicts an embodiment in which not only the optics components ofthe optics head 128 move together, but in which the optics head moveswith (is substantially rigidly coupled to) the optics arm 142. It isalso possible to provide embodiments in which, while components of theoptics head (preferably including at least the light source and theobjective) are non-movable with respect to each other, the optics headmay be movable with respect to some or all of the arm. For example, inthe embodiment of FIG. 11, the optics head 128 may be coupled to the arm142 by a movable or flexible, preferably resilient, leaf member 242. Theleaf member 242 may include all or part of a flexible printed circuit(flex-circuit) device e.g. for providing signals to and from the opticshead 128. A number of flex circuit materials or devices can be used. Oneexample is a flex circuit using a substrate including a polyimidematerial such as that sold under the trade name Kapton®, available fromE. I. du Pont de Nemours and Company of Wilmington, Del., with one ormore copper traces or regions and/or one or more electronic componentsformed or mounted thereon. Preferably, movement of the head 128 withrespect to the arm 142 can be positively controlled, such as by using avoice coil 244 or other electromagnetic or electronic device for movingthe head toward or away from the arm 142.

FIGS. 3–5 depict an optical head 328 according to one embodiment of thepresent invention. In the depicted embodiment, an objective lens 312 ispositioned by a lens mount 314 over a quarter wave plate 316. In someembodiments, some or all functions of the quarterwave plate can beprovided by a coating, rather than a plate. The lens mount can be formedof a number of materials including steel, glass, or silicon. The quarterwave plate can be formed of a number of materials, including mica andquartz. In some embodiments the functionality of a quarter wave platecan be provided by a coating. Below the quarter wave plate 316 is aoptical element unit, referred to herein as a periscope 318. Theperiscope 318 is substantially transparent, at least at the wavelengthof the laser light, and defines a first angled (preferably 45° anglewith respect to vertical) surface 322 acting substantially as a mirror,as described more thoroughly below. Preferably the 45° surface 322 willbe coated with a substantially reflective coating such as aluminum orreflective chrome coatings. The periscope 318, in the depictedembodiment, also includes an interior polarization beam splitter surface324 also preferably at about 45° (with respect to vertical) which issubstantially reflective (i.e. acts substantially as a mirror) for lightwith a first polarization and substantially transmissive for light witha second polarization. The periscope block can be made from a number ofmaterials, including, e.g., fused silica or SF2 (flint glass).

Below the periscope 318 is an optical die or “optical element unit”(OEU) 326. Use of the term “die” represents a convenience, and shouldnot be taken as limiting the invention to only the depictedparallelepiped, parallelogram or other shapes depicted herein. The OEU326 is provided with lenses, gratings, holograms, and/or other opticalcomponents or devices, as described more thoroughly below.

The OEU 326 is coupled by spacer blocks 332, 334 to an underlyingsub-mount 336 (preferably sliced from a silicon or similar wafer, asdescribed more thoroughly below). In the depicted embodiment, thesub-mount 336 is positioned on a printed circuit board 338 or flexcircuit.

The light path has its origin in the laser diode 612 mounted, withrespect to the sub-mount 336, e.g., using a laser mount 614. In oneembodiment, the laser beam is not collimated but follows a divergingconfiguration substantially from the laser source to the objective lenswhich forms a finite conjugate imaging system. In this configuration thebeam-forming or beam-shaping optics are provided principally for fullyor partially circularizing the light and/or fully or partiallycorrecting astigmatism and/or providing a beam pointing adjustmentfunction. One potential advantage of a finite conjugate (point-to-pointimaging system) is that the substantial demagnification provides aneffective reduction or elimination of the astigmatism that arises fromthe laser. However, circularizing lens 352 a may create sufficientastigmatism that a second lens or other optics 352 b may be advisablefor correcting astigmatism. It is also possible to position beam-shapingor other lenses or other optics on the surface of the submount 336between the laser and the mirror block 332, e.g. for circularizing orother optics purposes. In one embodiment lenses or similar optics 352 a,b along the optical path are configured to at least partially correctfor angular errors in the mounting (and thus the beam direction) of thelaser diode.

In the depicted embodiment, the laser diode is a side-emitting laserdiode and the horizontal laser beam 616 output by the laser diode 612 isreflected to a vertical beam by a 45° surface 618 positioned withrespect to the sub-mount 338 preferably by being incorporated as asurface of one of the spacers 332. In one embodiment, a portion of theemitted laser beam is reflected back (e.g. from the OEU 326) forpurposes of monitoring and controlling laser power output. In oneembodiment, the laser is a red-light laser. Preferably, however, thepresent invention can accommodate the use of shorter-wavelength lasers,such as blue-light lasers, (e.g. for achieving decreased spot size andincreased data density) while still retaining the same generalconfiguration of the optical head as used with red-light lasers (such asconfigurations having substantially all optical components movingtogether, mounted at one end of the optical arm, formed of one or moreoptical-element plates, each with multiple optical elements, and/ordefining an optical path with the majority of the length through a glassor other solid substance), although some details (such as shape or powerof lenses or other optics, pupil size, etc.) may be changed toaccommodate short-wavelength light.

As depicted in FIG. 16, the use of surface 618 for turning the beam froma horizontal beam 616 to a vertical beam could be eliminated from thedesign by providing a laser which is not side-emitting, such as avertical cavity, surface-emitting laser (VCSEL) 1612 (e.g. as describedin U.S. patent application Ser. No. 09/315,398, supra) which can beconfigured or positioned to emit substantially in a vertical direction1614. VCSEL's are also useful because of the substantial circularity ofthe beam and reduction or elimination of astigmatism.

As depicted in FIG. 7, in one embodiment the sub-mount 336 is formedfrom a small (“sliced”) portion of a larger silicon (or other) wafer 712(FIG. 7), with the wafer being formed, using typical wafer fabricationtechniques, preferably including a plurality of other electroniccomponents forming portions of some or all of the drive circuitry 112such as a high frequency laser modulator, pre-amp, laser diode driver,photodetector and associated circuitry, power or control circuitry,tracking or focus servo, data read/write electronics and the like. Awafer 712 formed with a plurality of silicon “chip” regions (which willbe separated, e.g., by sawing or slicing, as described below) then hasmounted on it, e.g. using optically guided pick and place technologiesor the like, a plurality of laser diodes and mounts 714 a through 714 xand a plurality of spacer bars with integrated mirrors 716 a,b,c. Eachspacer bar 716 contains a plurality of 45° mirror surfaces (718 a, 718b, 718 c, etc.). The laser diode 714 and mirror 718 of the spacer bar716 are positioned on the wafer 712 with respect to the electronicsthereon so as to provide for coupling of the laser to laser powercontrol or similar circuitry and to provide for substantial alignment ofthe output beam of the laser with a corresponding mirror 718. After thedesired components are positioned on the wafer 712, the wafer is slicedor sawed, e.g., along a plurality of lines (depicted, in FIG. 8, inphantom, 812 a,b,c, 814 a,b,c). As shown in FIG. 8, preferably, the sawlines 812 abc are positioned so that each resultant chip has left andright spacers 332, 334, resulting from right and left (respectively)portions of sawed spacer bars 716. In the resultant configurationdepicted in FIG. 9, each chip 912 has mounted, thereon, in a desiredconfiguration, or alignment, a laser diode 714, a turning mirror 618 andspacers 332 334, preferably with sufficient area 914 on the chip 912remaining to accommodate various electronic components formed as part ofthe wafer 712.

Although a number of shapes and sizes of devices can be used accordingto the present invention, in one embodiment, the sub-mount 336 has alength 512 of about 5 mm and a lateral dimension 412 of about 1.5 mm.

The optical die or optical element (“OE”) block 326 which is to bepositioned above the sub-mount 336 (and spaced therefrom by the spacers332, 334) can have a number of different configurations, depending onthe desired functions. In the embodiment depicted in FIG. 3, the OEU 326includes a plurality of beam shaping optics 352 and servo optics 354. Inone embodiment, the beam shaping optics 352 a, b are provided as (orperform functions substantially similar to those of) toric orcylindrical lenses, e.g., for fully or partially circularizing the laserbeam, correcting astigmatism and the like. Preferably, the optics areconfigured to control the overfilling of the objective as desired, e.g.to balance crosstalk with optical efficiency.

The optics 352 a,b, 354 can be lenses or similar refractive optics,gratings or holograms or other diffractive optics and the like. In someembodiments, optics may be formed in the optical die by etchingtechniques including providing approximate stepped shapes, continuousshapes, segmented or “telescoped” lenses, Fresnel lenses, and the like.In general, refractive optics are preferred, when otherwise feasible,because of the relatively higher sensitivity of diffractive optics towavelength.

The OEU is preferably a substantially planar (rectangularparallelepiped) block located between the substrate or submount and theperiscope. The OEU is provided with a plurality of optical elements orcomponents, whose configuration, fabrication, function and position maybe different in different embodiments. FIG. 18 illustrates an embodimentin which the OEU 1802 includes a forward sense optic 1804, a servooptical element 1806, beam-shaping optics 1808, 1810, patternedabsorptive coatings 1812, patterned reflective coatings 1814,anti-reflective coatings 1816 and alignment marks 1912, 1914 (FIG. 19).

As depicted in FIG. 18, the forward sense optics 1804 can be used fordeflecting some of the outgoing laser light back 1820, 1826 towards adetector 1828, e.g. mounted on the silicon or substrate 1830. Thefunction of the detector 1828 is to provide an indication of outgoinglaser power, e.g. for use in a control or servo-circuit to maintaindesired read and write power levels of the laser 1832. Those of skill inthe art will understand how to use signals from the detector 1828 forcontrolling power at the laser 1832. The forward sense elements 1804 canbe, e.g. a reflective hologram (e.g. an etched surface-relief hologramshown, in FIG. 18, on the top surface of the OEU 1802), with or withouta further reflective coating such as chrome or aluminum. It would bepossible to position the reflective optics or forward sense optics 1804in other locations such as on a bottom or other surface of the periscope1836 or the bottom surface 1848 of the OEU. It is also possible toprovide forward sense optics 1804 as a transmissive hologram or gratingwhich deflects light to a detector mounted at a location other than thesubstrate 1830, such as being mounted on the top surface 1838 of theperiscope 1836. It is also possible to provide forward sense optics 1804in the form of a prism, such as an etched prism, or a mirror surface, todirect light towards a detector 1828 mounted on the substrate 1830 orelsewhere.

In the embodiment of FIG. 18, the OEU 1802 also includes a servo-opticelement (“SOE”) 1806. The servo-optic element 1806 acts to modify lightreturning from the disk 1842 and/or direct the returning light to one ormore detector arrays 1844 for the purpose of generating useful trackingsignals, focus signals and/or data signals (e.g. as described morethoroughly below). The SOE 1806 may be a hologram or may be a formed oretched refractive element. Although FIG. 18 depicts the SOE 1806 on theupper surface 1846 of the OEU 1802, it is also possible to position theSOE on the bottom surface 1848 of the optical element unit 1802. It isalso possible to provide embodiments in which more than one opticelement is used for modifying light returning from the disk such asproviding for two or more lenses, gratings, holograms and the like. Itis also possible to provide embodiments in which one or more SOEelements are positioned other than on the OEU 1802, such as beingpositioned on a surface of the periscope 1836. The SOE 1806 may be, forexample, a cylindrical or toric lens, e.g. of the type commonly used inconjunction with a quadrant detector in the so-called astigmatic focusscheme. Refractive elements can be fabricated by etching, pressing,machining or molding and can be coated or uncoated.

The beam-shaping optics 1808, 1810 may be refractive and/or diffractivecomponents placed in the path of the outgoing beam e.g. to modify theangular divergence of the laser beam, e.g. specifically to achieve adesired beam intensity profile at the pupil 1852 of the objective lens1854. The relationship between the size and intensity-profile of thelaser beam as it reaches the objective lens 1854, with respect to thesize and shape of the objective lens 1854 affects the shape of thefocused spot at the disk 1856, and hence the ability to resolve datamarks, and affects the amount of track-to-track and in-track cross-talk.When the laser source 1832 is a edge emitter laser diode, as depicted,the laser beam, initially, will be generally in the form of anelliptical Gaussian beam. The beam, as it reaches the objective lens1854 will have one elliptical axis substantially tangential to the disctracks and the other elliptical axis substantially radial to the disktracks. The intensity of the laser light at the circumference of theobjective lens 1854 in the radial and tangential directions (expressedas a percentage of the central beam intensity) are referred to as therim intensities in these directions. A particular drive design may placelower or upper limits on rim intensities. In at least some embodiments,and especially in the case of low power drives, e.g. for portabledevices, there may be a constraint to provide a relatively high amountof light or percentage of light reaching the disk from the laser. Inthese cases, lower rim intensities are generally preferred since this isindicative that overfilling the lens is being substantially avoidedthus, avoiding the spilling or wasting of light energy. In oneembodiment the rim intensity is not greater than about 80% in thetangential direction and/or not greater than about 40% in the radialdirection (compared to the central or maximum intensity). In oneembodiment the rim intensity is preferably not less than about 50% inthe tangential direction and/or not less than about 15% in the radialdirection. In the limit of low rim intensities, all of the availablelight is passed by the lens. Accordingly, in at least one embodiment,the beamshaping optics 1808, 1810 are configured to assist in modifyingthe beam to achieve the desired intensity (or other) profile at the lens1854. In at least one embodiment, one or both of the beamshaping lenses1808, 1810 are anamorphic, aspheric elements. In one embodiment,beamshaping elements 1808, and/or 1810, are designed or configured insuch a way that the beamshaping elements 1808, 1810 can be omittedwithout creating the need for substantially modifying or adding otheroptical elements 1804, 1806, 1812–1816, 1828, 1836, 1854, 1858 ormodifying and/or moving the laser diode 1832, fold mirror 1858, prisms1838, reflecting surfaces 324, or photo diodes 1844. Those of skill inthe art will understand how to shape and position surfaces of such abeamshaping element, after understanding the present disclosure. Oneexample of a beamshaping element having this characteristic is describedby the following equation which expresses, for first and secondsurfaces, the amount of sag, in millimeters, as a function of the(orthogonal) X and Y radial positions, in millimeters, with the valuesof the equation parameters for the first and second surfaces being shownin Table I. The distance from the source point to the first surface is0.390 mm and the distance from the first to the second surface is 0.745mm in a material whose index of refraction is 1.96.Sag(X,Y)=C ₂₀ X ² +C ₀₂ Y ² +C ₄₀ X ⁴ +C ₂₂ X ² Y ² +C ₀₄ Y ⁴  (1)

TABLE I For First Surface For Second Surface C₂₀ −0.39159485−0.052783359 C₀₂ 1.93044042 0.63270121 C₄₀ 0.33426195 0.034762591 C₂₂−10.209495 −0.91998271 C₀₄ −6.7032532 1.7905847FIGS. 30A, B and 31A,B illustrate X and Y sag profiles 3012 a,b; 3112a,b of Equation (1) and Table I.

In general, in order for a beamshaping component to have the desiredcharacteristics in the context of a read/write device as describedherein, the position and/or shape of the beamshaper surface or surfacesmust be accurate to within a tolerance of less than about 5% preferablyless than about 3%.

In one embodiment, the beamshaper is formed by an etching process. Onesurface of a fused silica or other block of optical material is maskedwith one or more photomasks, including, in one embodiment, a gray-scalemask. Those of skill in the photo lithography art will understand how toform desired masks and perform effective etching. The masked block(which may be an area of a larger block or wafer, to be later cut ordiced) is etched, using a chemical etch, electron beam etch or othertype of etching known to those of skill in the art. After etching theshape, position and/or optical characteristics of the first beamshapersurface, formed as a result of such etching, is measured. Surfaceprofile of an optical surface may be measured by commercially availableequipment such as noncontact optical profilometer or a stylusprofilometer or scanning confocal microscope. The results of themeasurement are analyzed such as by comparing with digitized or otherdescriptions of the desired or ideal beamshaper surface shape and/orposition, and the results of this comparison are used to design,calculate and/or select (e.g., from among a plurality of pre-designedoptions) a shape and/or position for a second beamshaper surface whichwill have the characteristic of at least partially compensating for anydetected shape or position errors in the first beamshaper surface. Thoseof skill in the art will understand how to design a second opticalsurface so as to compensate for measured errors in a first surface. Asone simplified example, FIG. 32 illustrates the path of an ideal firstray 3212 a,b,c and its perfect refraction at a first lens surface 3214and a second lens surface 3216, with the source point 3218 unchanged.FIG. 32 also illustrates the path of a second ray 3222 a,b,c and itsimperfect refraction at the first lens surfaces 3214 (i.e. deviatingmore than the first ray 3212 a,b,c). In the illustration of FIG. 32,this type of refraction at the first lens surface 3214 is compensated byproviding refraction at the second surface 3216 which deviates thesecond ray such that the (apparent) source point is unchanged (i.e. suchthat the path of the second ray after the second refraction 3222 c, ifextended back, opposite its direction of travel, defines a (virtual)path 3224 which intersects the source point 3218). A photomask which isdesigned, configured and/or selected to result in the desiredcompensating second surface shape or position is applied to the second,opposed surface of the optical element unit and a second etching processis performed, resulting in an optical element unit having substantiallyaligned first and second beamshaper surfaces configured such that onebeamshaper surface at least partially compensates for imperfections orerrors in the other beamshaper surface. If desired, the secondbeamshaper surface may be etched substantially simultaneously with oneor more other optical elements.

In one embodiment, the second surface beamshaper elements are etchedafter the wafer is sawed, such that a different appropriate mask can bereadily applied to each optical element block to achieve the desired(compensating) shape and/or position. In another embodiment, a wafer isnot separated into individual OEUs until after second surface for theentire wafer has been etched. In this embodiment, it may be necessary toprovide a photo mask which may have different shapes, densities or othercharacteristics for forming second beamshaper surfaces in differentOEUs.

In one embodiment, the beamshaper is configured so as to providesubstantially no effect on the virtual source point for the laser source(or other source). In FIG. 28A, a beam 2812 is output by a laser 2814,may be affected by various non-beamshaper optical elements 2816 andimpinge on an objective lens 2818. The divergence and othercharacteristics of the beam 2812 define a virtual source point 2822,which is a point from which the beam 2812 appears to originate based ondivergence or other optical parameters. In practice, the beam 2812 mayhave divergence which is different along different cross-sectional axesand accordingly there may be more than one source point 2822. Forpurposes of the present description, source point 2822 can be taken asthe point which defines the greatest distance 2824 from the point to theobjective lens 2818. In the configuration of FIG. 28B, the optical pathcontains substantially the same elements (having an objective lens 2818,laser 2814 and (substantially identical) non-beamshaper optics 2816) butalso includes a beamshaper 2826. The beamshaper 2826 illustrated in FIG.28B is not intended to illustrate the actual shape or curvature ofbeamshaper lens surfaces. In the embodiment depicted in FIG. 28B, thevirtual source point 2822 is the same (i.e., is the same distance 2824from the objective lens) regardless of whether the beamshaper is present(as in FIG. 28B) or absent (as in FIG. 28A).

Although in the embodiment of FIG. 18, the outgoing beam 1858 passesthrough two optic elements 1808, 1810 formed on opposite surfaces 1846,1848 of the OEU 1802, it is possible to provide embodiments in whichonly one beam-shaping or other optic element is positioned in the OEU1802 in the path of the outgoing beam 1858. It is also possible toprovide embodiments in which one or more refractive or diffractiveelements for affecting the outgoing beam are positioned on the periscope1836, such as on a lower surface region 1862, an upper surface 1864,(which, in the depicted location, would also be in the path of thereturning beam), an angled reflective surface 1866 (also in the returnbeam path) and interior surface 1868 (also in the return-beam path) andthe like. Optical elements in the path of the outgoing beam can alsoperform useful (or vital) functions other than (or in addition to)controlling the rim intensities. Beam-steering optical elements can beprovided to correct laser beam pointing errors (e.g. errors arising fromoff-axis mounting of the laser diode 1832 and the like). It is alsopossible to provide at least partial correction of pointing errors bytranslating or rotating the OEU 1802 in tangential and/or radialdirections. This approach is facilitated when the beamshaper optics haveoptical power in both directions (tangential and radial). In general,the range of beam steering adjustment is at least partially limited bythe wave-front error that is induced by the position error (whichdegrades the spot profile at the disk and the data and servo signals).Another function that can be achieved by diffractive or refractiveoptics in the outgoing beam path is correction of laser diodeastigmatism. Since the surfaces are generally aspheric, some astigmatismmay be designed-in to cancel that which is typically inherent in lasersources such as laser diodes.

In some embodiments, portions of surfaces of the OEU 1802 (or othercomponents, such as the periscope 1836) are coated with an absorptivecoating 1812 patterned on the top 1846 or bottom surfaces 1848 (or onthe side or end surfaces). Absorptive coatings can be used to controlthe path of unwanted light within the optical head. With the laser anddetectors in relatively close proximity, and in close proximity withmany surfaces that may have varying reflectivities (including thesubstrate 1830, surfaces of the OEU 1802, periscope 1836, lens 1854 andlens mount and the like), there is a potential for unwanted lightreaching optical detectors 1844, 1828 causing erroneous signals ofvarious types such as a focus or tracking offset. In some embodiments,substantially all surfaces which are not designed to permit passage ofdesired light are coated with a absorptive (or reflective) coating. Inanother approach, optical ray-tracing (or empirical observation) candetermine likely paths of undesired light and locate optimum placementof areas of black (or low reflectance) material designed to minimizeunwanted signals.

A number of materials can be used as an absorptive coating such as asingle layer of a highly absorbent material such as germanium orsilicon. If desired, such absorptive layers may be provided with anadditional coating such as an anti-reflective coating to further improveperformance. In some embodiments, the absorptive coating may be amulti-layer absorber/anti-reflector (e.g. chromium/anti-reflectormulti-layers).

In some embodiments, some regions of the OEU (or other components) maybe provided with patterned reflective coatings 1814. These may bepositioned and configured to perform functions similar to those ofpatterned absorptive coatings described above. Patterned reflectivecoatings may be used to deflect unwanted light which would otherwisefall on detectors. In addition, reflective coatings may be used to helpdirect light towards a detector such as in the case of the forward senseoptic 1804. Reflective coatings can be made from a number of materialshaving appropriate reflectance and adhesion, including single-layer ormulti-layer coatings of metals or metal alloys such as aluminum, gold,silver, chromium, and the like or from single or multilayer dielectriccoatings. Other materials for use as reflective coatings will beunderstood by those of skill in the art after understanding the presentdisclosure.

In some embodiments, anti-reflection coatings are provided on selectedsurfaces or portions thereof, e.g. to reduce reflections which may causeunwanted signals on detectors and/or to reduce the amount of reflectiveloss of optical power in the system. In general, anti-reflectivecoatings may be used on surfaces which are not in optical contact withother surfaces of the same refractive index. In such cases, in theabsence of anti-reflection coatings, there is always some reflectionloss. For example, typically a glass-air interface reflects about 4percent of the light (at normal incidence). In a case where the OEU 1802is solder-pad bonded to the periscope 1836, a gap (typically of a fewmicrometers) is present, which is filled with air, and unwantedreflections can occur unless anti-reflection coatings are applied. Inthe case where the optic block 1802 is substantially adjacent to theperiscope 1836 (e.g. in cemented or adhesive-bonded configurations),some or all of the optics 1804, 1806, 1810 may be formed by an etchingor similar process to provide regions which are recessed below the uppersurface 1846, thus creating an air gap. A number of materials can beused as anti-reflection coatings. In one embodiment, single ormulti-layer thin films, usually of a dielectric material such asmagnesium fluoride, applied in predetermined thicknesses, will reduce orsubstantially eliminate optical reflections over a specific wavelengthand angular range. Those of skill in the art will understand how toselect and apply anti-reflective coatings after understanding thepresent disclosure.

In some embodiments, to assist in optically aligning the OEU forassembly to the substrate or periscope, alignment marks 1912, 1914 areprovided. In some embodiments the alignment marks 1912, 1914 are sizedand shaped to overlap or complement corresponding marks on othercomponents, such as the substrate 1830 or periscope 1836, to facilitateprecise location, such as location to a precision of about 10micrometers or less. A number of materials and procedures can be usedfor forming alignment marks. In one embodiment, the alignment marks arephotolithographically-defined lines or targets which may be formedduring any of the other photolithographic steps in the fabrication ofthe OEU and/or etched or coated along with other components such as theforward sense element or the servo-optical element. The marks may be onthe top surface (FIG. 19) or bottom surface.

In some embodiments, substantially all of the optical components of theOEU are formed by patterned lithography and/or etching in glass (orother optical material), possibly in conjunction with a variety ofcoating steps. Such processes are typically suitable for processing at“wafer scale” i.e. a relatively large (e.g. 3 inch to 6 inch diameter)wafer of glass or optical material may be lithographically patterned todefine a large number of individual parts, each part being on the “chip”scale (such as around 1 mm to 5 mm, or smaller). All of the individualparts on the wafer may be processed simultaneously (etched, coated,etc.) leading to low-cost individual parts. Further cost reduction isprovided by forming multiple optical elements 1804, 1806, 1808, 1810) ona single block 1802 using photolithographic or similar techniques, suchthat the relative positioning of the optical components on the block1802 are predefined and provided with a high degree of precision. Inthis way, it is possible to avoid the cost of aligning individualoptical elements during device fabrication (which can be an expensiveprocedure, particularly for small-scale devices such as devices havingmultiple optical elements on the scale of about 1 mm to 5 mm).

Preferably the OEU 326 is formed of a glass or plastic (e.g.polycarbonate, acrylic and the like) with the optics formed therein inpredefined positions prior to assembly. Glass is preferred, whenotherwise feasible, because it is relatively insensitive to temperatureand water absorption (or other chemical attack) and can be joined toother components using higher temperature techniques such as solderreflow. In one embodiment, the OEU 1802 is joined to the periscope 1836by an adhesive. Preferably, one or both of the interface surfaces suchas the upper surface 1846 of the OEU 1802 has one or more channels ormoats 2102, 2104 formed therein, e.g. by saw cuts or the like (FIG. 21).In one embodiment the width and depth of each moat is about 100micrometers. In one technique, after the upper surface 1846 is placed inthe desired alignment and positioned adjacent the lower surface of theprism or periscope 1836, an adhesive is introduced along the edges 2106,2108 and allowed to “wick” or flow by capillary action, inwardly 2110,2112. The moats 2102, 2104 receive any excess adhesive and prevent theadhesive from flowing inwardly substantially beyond the locations of themoats 2102, 2104 (since adhesive, inward of the moats 2102, 2104, couldpotentially interfere with the lenses 1810 or other optics).

In one embodiment, the optical die 326 is placed in the desired operableposition with the aid of light from the laser diode 612. In thisembodiment, the laser diode is connected to at least power and controlcircuitry prior to mounting of the optical die 326 and the siliconsub-mount 336 can be provided with power sufficient to provide the laserlight output from the laser diode 612 and, optionally, to detect signalsat a photo-diode or similar detector array (including those on thesubmount 1830). In one embodiment, positioning equipment for placing andmounting the optical die with respect to the submount 1830 involvesmonitoring characteristics of light transmitted through one or both ofthe beam shaping optics 352 a,b and/or servo optics 354 as the opticaldie 326 is moved and positioned. Preferably, the optical die 326 ismounted with respect to the spacers 332, 334 using well known techniquessuch as solder reflow. By using a procedure in which the optical die ispositioned while light is being emitted from the laser (or other lightsource), and in which the position and/or focus or other characteristicsof the light is used to guide optical-die-positioning equipment(preferably in a substantially automatic fashion, such as by usingdetected light to define a servo or control signal for the positioningequipment), the positioning of the optical die can at least partiallycompensate for various inaccuracies in the position of the laser (orother light source).

It is also possible to use an active alignment technique (i.e. usinglight from the laser to help in component placement, during fabrication)to at least partially compensate for inaccuracies in the relativeposition of the laser (or other light source) with respect to thephotodector(s) 356. In one embodiment, after the optical die ispositioned and fixed, the periscope block, preferably with the objectivealready mounted thereon, is positioned using active alignment. In oneembodiment, a mirror is positioned near the objective (e.g. to mimic thereflection from the optical disk) and the periscope block is moved untilthe reflected light forms a desired or closest-fit pattern with respectto the photodetector(s). In at least one embodiment, it is believed thatmoving the periscope block is most feasible for positioning thereflected beam in a lateral direction (i.e. a direction perpendicular tothe longitudinal axis of the optical arm). Accordingly, it is believeduseful, in at least some embodiments, to select a type or configurationof photodetector(s) which is relatively insensitive to inaccuracies ofbeam placement in the longitudinal direction. In that way, the activealignment technique can be used to position the periscope block so as toprovide the greatest accuracy of beam placement in the lateraldirection, where the photodector(s) are most sensitive to inaccuracies.

Although it is possible, in some configurations, to position the opticaldie 326 prior to positioning of other components (such as the periscope318, lens 312 and the like), in another embodiment, it is also possibleto separately assemble some or all of the periscope 318 quarter waveplate 316, and/or lens 312 and the like to the optical die 326 prior tomounting the optical die 326 with respect to the spacers 332, 334.Regardless of the order in which the various components are aligned andmounted, embodiments of the present invention are believed to providesubstantial benefits arising from employing wafer scale assemblytechniques and/or multiple layer (stacking) assembly techniques tofabricate the optical head. By providing a relatively inexpensive andpractical fashion for assembling an optical head to achieve a desired(and substantially static) alignment between components, the assembly ofthe entire drive 112 is simplified since critical alignment has alreadybeen performed during assembly of the optical head and relatively lesscritical or higher-tolerant assembly of the head to the arm 142 can beachieved, e.g., in a drive manufacturing or assembly plant at relativelylow cost.

The periscope 318 is mounted, e.g., using solder reflow, adhesive orsimilar assembly techniques, to position the periscope mirror 322 in thedesired position with respect to the optical die beam shaping optics 352ab so as to reflect the beam in a horizontal direction 358, i.e.,substantially parallel to the data surface of the disk 362. Thepolarization beam splitter 324 is, in the depicted embodiment,substantially parallel to the periscope mirror 322 (i.e. substantiallyat about a 45° angle with respect to vertical) and may be formed by acoating (PBS coating) placed on a surface of a first block of theperiscope 318 preferably with the coated surface mating with a surfaceof an end block 364 of the periscope 318. The PBS 324 is selected orapplied in such a fashion that the PBS will be substantially reflectivewith respect to the polarization of laser light as it arrives at the PBS(“first polarization”). Those of skill in the art will understand how toselect or control polarization or polarization beam splitters in thisfashion.

Accordingly, the PBS reflects the laser beam in a vertically upwarddirection (i.e. towards the disk 362, 366). The beam travels through thequarter wave plate 316 and thence through an objective lens 312 alignedwith the quarter wave plate by the lens mount 314. The objective lens312 is configured to substantially provide the desired spot size (focus)with respect to the read/write surface of the (preferably first surface)disk 362.

Although a number of sizes and shapes of devices can be used inaccordance with embodiments of the present invention, in the depicteddevice, the height 514 from the printed circuit board 338 to the lens314 is about 2.9 mm. In one embodiment, the distance from the objectivelens 312 to the surface of the disk 362 (defining the working distancefor the optical system) is about 0.3 mm.

After reaching the disk 362, and depending on the portion of the diskilluminated and whether a data bit is present or absent at thatposition, light reflected from the disk 362 passes vertically downwardto the objective lens 312 and quarter wave plate 316. At this point(e.g. because of passage twice through the quarter wave plate 316),polarization of the reflected light as it reaches the PBS coating isdifferent from the first polarization and the PBS coating 324 isconfigured to allow substantially all of the reflected light to passthrough the PBS coating and continue vertically downward, through theservo optics 354 and to the photo detector array 356.

A number of types of photo detector array can be used including quadrantdetectors, φ detectors and the like, and the type of servo optics 354will be selected corresponding to the type of detector being used, aswill be understood by those of skill in the art after understanding thepresent disclosure.

In one embodiment, the substrate 1830 is provided with first and second(“A” and “B”) optical detectors 2201, 2202 (FIG. 22) for detectingreflected light for use in providing focusing, tracking and/or datasignals. In the depicted embodiment, each detector array includes threebar-shaped parallel detectors 2211, 2212, 2213, 2221, 2222, 2223. Oneadvantage of the detector configuration having three parallel,bar-shaped detectors in the detector array, is that the output isrelatively insensitive to the placement of or position of the beam in alongitudinal direction 2210. This means that there is relatively highertolerance, during fabrication, for misalignments of optical components(mounting of the laser 1832, OEU 1802, periscope 1836 and/or lens 1854)which results in movement or misalignment of the reflected beam (at thedetectors) in the detector longitudinal direction 2210, compared tothose misalignments that cause movement or misalignment with asubstantial component in a lateral direction (perpendicular to thelongitudinal direction 2210). Relaxing tolerance requirements for atleast some alignment parameters can assist in lowering fabricationcosts.

Providing a two-detector scheme 2201, 2202 permits the use of adifferential detection approach. Differential detection generallyprovides improved performance compared to non-differential (singledetector array) schemes, at least in terms of reduced cross-talk(tracking-to-focus cross-talk or offsets resulting from distortedbeams), since differential schemes tend to reject common-mode noisebetween the detectors. In one embodiment, tracking-to-focus cross-talkis less than about 0.25 micrometers peak-to-peak (p—p), preferably lessthan about 0.1 micrometers p—p. In one embodiment, track-to-trackcross-talk is less than about 5%, preferably less than about 2%. Atwo-detector scheme working configuration as shown in FIG. 22 can beimplemented by providing an SOE 1806 configured for receiving thereflected (“return”) light beam 1842 and creating first and secondreflected beams 2302, 2304, e.g. as depicted in FIG. 23. As shown inFIG. 23, the first and second beams 2302, 2304 are directed so as tofall on regions of the first and second detectors 2201, 2202 (FIG. 22)respectively, defining first and second footprints of the beams 2203,2204 thereon. Preferably, the first and second beams 2302, 2304 havedifferent optical characteristics such as having different focal pointor focal plane locations. It is possible to configure differentialoptical systems with the focal points of the first and second beamsrespectively on opposite sides of the detector plane 2314. In theembodiment of FIG. 23, however, both focal points 2306, 2308 are on thesame side of the plane 2314 of the detectors 2202, 2201. The opticalcharacteristics of the first and second beams 2302, 2304 differ byhaving the respective focal points 2306, 2308 at different locations,such as different distances, 2310, 2312, respectively, from the plane2314 of the detectors. Providing different focal points 2306, 2308 ofthe first and second beams 2302, 2304 can be useful in a differentialdetection scheme for a number of reasons.

In one embodiment, a focus error signal (“FES”) for each of thedetectors 2201, 2202 is obtained by combining signals from each of threeparallel bar-shaped detector regions in each of the detectors 2211,2212, 2213, 2221, 2222, 2223. According to one embodiment, a focus errorsignal for the first or “A” detector 2201, termed “FES_(A)”, is obtainedby combining the negative or inverse of the signals from the outermostregions of the first array, i.e. A₁ 2211 and A₃ 2213 with the signalfrom the central region A₂ 2212. Expressed algebraically,FES_(A)=A₂−(A₁+A₃). Similarly, in this embodiment, a focus error signalfor the second detector 2202 can be expressed as FES_(B)=B₂−(B₁+B₃). Itcan be seen that, in this fashion, the two FES signals from the twodetectors 2201, 2202 are related to the sizes of the footprints of thebeams 2203, 2204 which impinge on the detectors 2201, 2202. The sizes ofthe footprints 2203, 2204 will vary depending on the degree or amount offocus of the light spot on the medium 1856 (FIGS. 18), e.g., in apivot-focus apparatus, as the optical arm (or a portion thereof) pivots224 (FIG. 2).

FIGS. 24A and 24B are graphs depicting the magnitude of the FES_(A) andFES_(B) signals 2402 a, 2402 b, respectively, as a function of themagnitude or degree of focus at the medium. In one aspect, focus can beexpressed as the distance 1862 (e.g. in micrometers) of the objectivelens from the information layer 1864 of the medium 1856. One effect ofproviding different distances 2310, 2312 for the focal points 2306, 2308of the first and second beams 2302, 2304 is that the configuration ofthe FES signals from the two detectors 2201, 2204, as a function offocus are different, e.g. as can be seen by comparing FIGS. 24A and 24B.Each of the individual FES signals 2402 a, 2402 b is substantiallynon-linear (highly curved) in the regions 2406 a, 2406 b near thedesired or nominal focus. Such non-linearity makes it relativelydifficult and/or inaccurate to use either of the focus error signalsFES_(A), FES_(B) alone, as a control signal for controlling focus.However, as depicted in FIG. 25, when the negative or inverse 2404 ofthe FES_(B) signal 2402 b is combined with the FES_(A) signal 2402 a,the resultant combined focus error signal FES_(A)−FES_(B) 2502 issubstantially linear in a capture range 2504 located about the nominalfocus point 2506. Thus, the differential scheme as depicted, providingtwo different focus point distances, 2310, 2312 (in the depictedembodiment, both on the same side of the detector plane 2314) can assistin providing a substantially linear differential focus error signal, atleast in a capture region 2504 which can be used for controlling a focusmotor or actuator. In one embodiment, the capture region is the regionwithin ±10 micrometers of the nominal focus. In one embodiment, thecombined focus error signal FES_(A)−FES_(B) 2502 has a maximum departurefrom linearity (e.g. departure from a best-fit linearity) at any pointwithin the capture region of less than about 10%, preferably less thanabout 2%.

In a similar fashion, a combined tracking error signal can be defined asTES=(A₁−A₃)+(B₁−B₃), and a combined data signal can be defined asData=(A₁+A₂+A₃+B₁+B₂+B₃). In one embodiment, the combined focus errorsignal TES has a maximum departure from linearity (e.g. departure from abest-fit linearity) at any point within the capture region of less thanabout 10%, preferably less than about 2%.

If desired, both the FES and TES can be normalized to the total power ineach signal, e.g. to reduce the effect of a signal amplitude change(such as due to disk reflectivity differences or beam vignetting, e.g.over actuator stroke, or similar effects). For example, normalized FESand TES signals can be provided asFES_(normal)=[(A₁+A₃−A₂)/(A₁+A₂+A₃)]−[(B₁+B₃−B₂)/(B₁+B₂+B₃)] andTES_(normalized)=[(A₁−A₃)/(A₁+A₃)]+[(B₃−B₁)/(B₁+B₃)]. The variouscombinations of signals from the regions of the two detectors can becombined in an analog or electronic fashion, or can be digitized andcombined digitally (or a combination of both approaches).

In one embodiment, the relative size of the central element in eachdetector 2212, 2222 can be adjusted to reduce the cross-talk of thetracking signal TES into focus signals FES for different detectorpositions with respect to the object lens and/or different groovegeometries of the medium 1856 (on media with a groove) or different pitgeometries on media with premastered pits.

FIG. 12 illustrates one example of a manner of providing forcommunication of electrical signals to and from the optical head 128.Although the embodiment of FIG. 6 provided for the submount 336 to bepositioned with respect to a printed circuit board 338, in theembodiment of FIG. 12, the submount 336 is accommodated in a cut-out1212 formed in a flex circuit (e.g. a Kapton®-copper flex circuit) 338′.The flex circuit 338′ is preferably electronically coupled to the opticshead 318 such as by forming wire bonds between optics head bonding pads1216 and flex circuit bonding pads 1218 The flex circuit 338′ can bephysically coupled e.g. by an epoxy or other adhesive, such as that soldunder the tradename Epo-Tek H70E-2, available from Epoxy Technology,Inc. of Billerica, Mass. Some or all of the flex circuit or othercomponents may be coated or encapsulated, e.g. for protection. The flexcircuit 338′ preferably contains some or all electronics used forcontrol and/or signal processing for the optics head 128. Other mannersof providing for electrical communications to and from the optics headwill be understood by those of skill in the art after understanding thepresent disclosure.

One of the significant factors in design of devices, according toembodiments of the present invention, relates to thermal management.Many laser diodes or other light sources can be significant heatsources. In addition, many electrical or electronic components, such aspower supplies or conditioners, resistors, diodes, and other items, canadd to the total heat load. It would not be unexpected to use a laserdevice having a power output near 200 milliwatts. Elevated temperaturecan damage, or degrade performance, of electronic components and/ormedia, both in a drive, and in a PED or other device which incorporatesa drive. Lasers and other components may have performancecharacteristics which change, sometimes radically, as a function oftemperature, and it may be difficult or expensive to adequatelycompensate for such changes. Further, products which perceptiblygenerate heat may have reduced commercial appeal. Previous electronic orelectro-optical devices commonly used relatively large, heavy orpower-consuming components, such as large and/or heavy heat sinks, fansand the like. The present invention, however, is preferably alow-profile (or otherwise small) device and is especially suited to(although not necessarily limited to) use in connection with PEDs orother small, lightweight, low-power devices. Accordingly, it ispreferred to configure the optical head in a fashion to avoidconcentrations or quantities of heat and/or to avoid elevatedtemperatures which might harm equipment or components or which mightdegrade performance. Preferably, in at least one embodiment, at least aportion of the underside of the flex circuit 338′ (preferably with theportion 1214 extending over some or all of the cut-out region 1212) hasa coating or layer of a thermally conductive material, such as copper,e.g. to act as a heat sink or heat dissipater. In one embodiment, thesubmount 614 (if present) is formed of a substantially thermallyconductive material, such as aluminum nitride or silicon carbide. Thesubmount has a relatively large surface area (e.g. compared to thefootprint of the laser diode 612 and/or mount 614) to effectively spreadthe heat, generated by the laser, over a relatively large surface area,avoiding concentrations of heat and undue (locally) elevatedtemperatures.

In addition to provisions for thermal management and electronic couplingof the optics head 128 to the arm 142, embodiments of the presentinvention also include provisions for mechanical mounting or coupling ofthe optics head 128 with respect to the arm 142. In the embodimentdepicted in FIG. 13, first and second arms 1312 a, b define a region1313 for receiving an optics head. A plurality of flexible prongs 1314a,b,c,d are coupled to the arms. The prongs have angled protrusions 1316a,b,c,d configured to contact portions of the optics head when the headis in the region 1313. Once the optics head is positioned as desired(e.g. using mechanisms for gripping and moving the optics head), theprotrusions can be fixed to portions of the optics head, e.g. using anadhesive, and preferably the prongs are stiffened or fixed, e.g. bycoating with epoxy or other stiffening agent, possibly using anultraviolet or other curing step.

FIG. 14 depicts an embodiment of the invention in which the detector1412 is positioned outwardly of the mirror block 332. In this embodimentthe PBS 1424 is positioned and configured to substantially reflect thelight 1426 received from the laser source 1428 to a horizontal path1432. The light is then reflected to a vertical path 1434 toward theobjective 312 by a reflective surface 1438. The reflected light returnsalong a similar path 1434, 1432, but, having a changed polarization, istransmitted through the PBS 1424 along a horizontal path 1442, to bereflected downward 1444 toward the detector 1412 by a reflective surface1446. In one embodiment the undersurface of the optics block 326′ in theregion surrounding the path of the reflected beam 1444 is coated with anabsorptive coating, such as non-reflective (black) chrome, to assist inprotecting the detector 1412 from stray light. In one embodiment, anannular reflective coating is positioned on the lower surface of theoptics block 326′ surrounding the position of the central portion of thebeam 1426 in order to reflect the outermost annular portion of the beamdownward 1446 to a feedback detector 1448 for controlling laser power.Other regions can be coated with absorptive or reflective coatings forcontrolling stray light, as will be clear to those of skill in the artafter understanding the present disclosure.

Another embodiment of the invention is depicted in FIG. 10. While FIG.10 shares some features with the embodiment of FIGS. 3–6, in FIG. 10 thesilicon (or similar) sub-mount 1036 on which the laser 1012 and detector1056 are mounted is positioned in a substantially vertical attitude,i.e. in a plane perpendicular to the surface or plane of the disk 1062.An optical die 1026 is mounted spaced from the sub-mount 1036 by spacers1032, 1034 and the turning mirror 1018 is a separate structure. Lightfrom the laser 1012 passes through beam-shaping optics 1052 ab and intoa mirror block 1022. The read/write beam is reflected by an interior PBSsurface 1024, downward through a quarter wave plate 1016 and objectivelens 1013 to the disk 1062. Reflected light, having its polarizationaltered, passes through the PBS 1024 and is reflected from a reflectivesurface 1023 through servo optics 1054 of the optics die 1026 to thephoto detector 1056. Although a number of sizes and shapes of devicescan be used in connection with the present invention, in one embodiment,the vertical height 1072 of the optics die 1026 and block 1022 is about1.8 mm and the height 1074 of the quarter wave plate and mounted lens isabout 1.02 mm. In one embodiment, the lateral dimension 1076 of theoptics die 1026 and block 1022, is about 4.0 mm.

Another embodiment of the present invention is depicted in FIG. 16. Inthe embodiment of FIG. 16, the laser 612 and the photodetector 356,rather than being mounted on a separate chip or submount, are mounted onthe lower surface of the optical die 326. In the depicted embodiment,regions of the lower surface of the optical die 326 are selectivelymetalized or coated, e.g. to provide reflective or absorptive regionse.g. for surrounding the photodetector 1512 to control stray light,and/or to define regions for coupling the photodetector 356, laser 612or other components or circuitry. In one embodiment one surface of thelaser diode is used for coupling leads 1514 and the like to providepower, data or control signals to and from the laser 612. In oneembodiment, the free surface of the laser 612 can be directly coupled toa heat sink (including, if desired some or all of the optical arm), foreffective thermal management. The configuration of FIG. 16 can not onlyprovide for effective thermal management, but, by avoiding the need fora silicon board 338 or submount 336, can reduce the vertical heightrequirements, further promoting the low-profile nature of the opticalhead.

Another embodiment of the invention is depicted in FIG. 26. In theembodiment of FIG. 26, a second beam splitting surface 2602 is providedas part of the periscope 2604 to provide for creation of first andsecond reflected beam paths 2606, 2608 for impinging on first and seconddetector arrays 2610, 2612. The embodiment of FIG. 26 can be comparedwith the embodiment of FIGS. 18 and 23. In FIG. 23, the SOE optic 1806performs two functions: splitting the reflected beam 1842 into first andsecond beams 2302, 2304 and providing two different focus pointdistances 2310, 2312. Since the extra beam splitting surface 2602(combined with the effect of the original beam splitting surface 324)results in two spatially-separated reflected beams 2606, 2608, it is nolonger necessary to provide servo optics configured for performing abeam splitting function of the type depicted in FIG. 23. If desired, itis also possible to dispense with modifying or changing the opticalpower applied to the two reflected or return beams 2606, 2608 (thusmaking it possible to eliminate altogether any need for servo optics orother optic devices for the return or reflected beam paths 2606, 2608).For example, differential size measurement can be arranged as depictedin FIG. 27 showing one returning beam forming a virtual focus 2702beyond the detector array 2612 and the second returning beam forming areal focus 2704 before the second detector array 2610. Since these foci2704, 2702 are natural images of the spot at the disk (at the samedistance from the disk as the apparent laser source point), noadditional focusing power is needed and thus the SOE may be eliminated.

One advantage of eliminating an SOE (e.g. such as in the embodiment ofFIGS. 26 and 27) is to assist in correction of laser pointing errors.When an OEU contains both outgoing beamshaper optics 1808, 1810 (FIG.18) and returning or reflected beam optics 1806, adjustment of the OEU1802, e.g. in order to correct a laser pointing error, will also movethe SOE 1806. Such movement of the SOE 1806 can cause error (potentiallyuncorrectable) in registration of the SOE 1806 and the detector arrays1844. If the SOE element 1806 can be eliminated, it is possible toadjust the mounting position of the OEU 1802, (e.g. to correct laserpointing errors) without also moving an SOE element. Any detectoralignment required can be performed by other means, such as translationof the objective lens 1854.

In light of the above description, a number of advantages of the presentinvention can be seen. Using embodiments of the present invention, it ispossible to provide a beamshaper in a practical and feasible fashionwhich leaves at least one optical parameter substantially unchanged, inthe optical path of a read/write device or other optical device,regardless of whether the beamshaper is present. The present inventionmakes it feasible to develop two or more optical path designssubstantially simultaneously (e.g one with a beamshaper and one without)while avoiding some or all costs associated with completely designingtwo different systems. The present invention makes it feasible toprovide different optical systems for accommodating variances incomponents (e.g. variations in laser characteristics), while reducing oravoiding costs associated with developing and using two or morecompletely different optical paths or systems. In one aspect it iseconomically feasible to provide a highly accurate beamshaper or otheroptical element by etching, or otherwise fashioning, one lens (or other)surface, measuring errors or imperfections in the shape or placement ofthe surface, and selecting, designing or modifying a second, alignedlens or other surface of the beamshaper so as to at least partiallycompensate for the errors or imperfections. Cost-feasibility can befurther provided or enhanced by at least partially forming severaloptical elements simultaneously in a single optical element unit orblock and/or by forming multiple optical element units simultaneously ona wafer (which is later sawed).

The present invention includes a recognition that a small spot sizecompatible with high data density (e.g. as facilitated by use of a firstsurface medium) makes it feasible to provide substantially all opticalcomponents in a small and/or lightweight package, e.g., such thattracking and/or focus can be performed by moving the entire opticspackage or head (as opposed to, e.g., moving just the objective lens).The present invention provides a device which is not only sufficientlysmall and lightweight to maintain all of the optics components in fixedpositions with respect to one another, but also to provide thesecomponents with spatial extends in various directions, such as providinga small vertical (low profile) optical head so as to be compatible withthe form factors of a type consistent with use in small and/or portabledrives or host devices, e.g., personal electronic devices. The presentinvention can provide an optical head which is highly efficient such asby using an optical design which substantially avoids overfilling orotherwise spilling optical or other energy. The present inventionprovides a design in which some or all steps of fabrication can beperformed in a relatively inexpensive fashion such as using techniquesfrom wafer-scale fabrication technology and/or using a planar orstacking technique for assembling the optical head. One characteristicof an optical device such as that disclosed herein which containsmultiple optical elements on various surfaces of one or more opticalelement units, is that the substantial majority of the optical pathlength from the laser source to the objective is through a solid (glassor other) medium, with only a minor portion being through air. In oneembodiment, the percentage of the optical path from the laser source tothe objective lens which is in a glass or other solid medium (as opposedto being through air) is greater than about 50 percent, preferablygreater than about 75 percent, and more preferably greater than about 85percent. In one embodiment, of a total optical path length (from thelaser to the objective lens) of about 5500 micrometers, about 5000micrometers of the path length is through the glass (or other solid)substance (e.g., the optical element unit 1802 and periscope 1836).About 450 micrometers of the total optical path is through air from thelaser to the OEU 1802, with other portions of the path, through air,potentially occurring at the interface between the optical element unit1802 and periscope 1836 and/or between the periscope 1836 (orquarterwave plate 316) and objective lens 1854.

The present invention provides a practical and feasible system in whichsubstantially all components of the optical head from the laser or otherlight source to the objective move together as a unit (e.g. for focusand/or tracking), i.e. in which substantially each optical component ofthe optical head is in a fixed location with respect to othercomponents.

In one embodiment, the optical head is based on a wafer-scalefabrication approach. Preferably, a silicon or similar wafer havingelectronics formed therein, in the normal fashion, has opticalcomponents stacked or otherwise positioned thereon, preferably at leastsome components being placed prior to slicing the wafer, to form theoptical components of the optical head. In one embodiment, a firstmirror/spacer level is positioned on the wafer and one or more levels ofoptics (generally proportioned similar to the proportions of the “chip”after wafer slicing) are positioned on the top of the spacers. In oneembodiment, alignment of some or all optical layers above the spacer isperformed while the laser source (preferably mounted on the wafer) isemitting laser light, and using the emitted laser light to assist inpositioning or alignment.

In one embodiment, the read/write beam travels through one of the opticslayers in a direction substantially parallel to the plane of the disk.Providing a configuration in which a substantial portion of the opticalpath is parallel to the plane of the disk assists in providing arelatively low vertical profile. By providing a system which can usewafer-scale fabrication and which can be fabricated by stacking discretecomponents such as spacers, optical components and the like, it ispossible to construct a small, high precision, low weight, low profileand/or small spot-size optical head at relatively low fabrication costs.As used herein, “read/write” refers to configurations that are used onlyfor reading and to configurations that are used for both reading andwriting.

In one aspect an optical head of a type useable in a optical diskreader/writer is provided. The optical head has a low profile, e.g., ina vertical direction parallel to the disk spin axis, such as less thanabout 5 preferably less than about 3 mm. Substantially all components ofthe optical system, including a laser source, objective lens,intervening optics and photo detector are provided in the optical headand mounted in a fixed position with respect to one another.Substantially all optical components of the optical head are moved as aunit, e.g., during tracking and/or focusing. Preferably, the opticalhead is fabricated using wafer scale and/or stacking technologies, e.g.,stacking substantially planar components to achieve the final opticalhead configuration.

A number of variations and modifications of the present invention can beused. It is possible to use some aspects of the invention without usingothers. For example, it is possible to provide a beamshaper such thatsome optical parameters are invariant regardless of whether thebeamshaper is used, without using an etch-measure-compensation procedureas described and/or without forming the beamshaper in a wafer scaleprocedure. It is possible to provide an optical head which issufficiently small and/or lightweight that it becomes feasible to movethe entire optical head (e.g. for tracking and/or focus) without usingthe wafer-scale and/or stacking fabrication techniques described herein.It is possible to use some or all aspects of the present invention inoptical devices other than the described optical disk read/write device,such as using the invention in connection with a non-first-surfacemedium, using the invention in a DVD, DVD-ROM, CD, CDR and/or CD-ROMdevice, digital cameras, video cameras, or similar devices, and/or usingthe invention, in general, in any optical device where it is beneficialto provide two or more different optical paths or designs while reducingor avoiding costs associated with designing or developing two or moreoptical paths or designs.

In one embodiment, some or all of the optics depicted as being providedin, or on, a separate optics die 326 can be formed in or on theperiscope or optical element unit 322, thus potentially making itpossible to provide embodiments of the present invention which do notrequire providing or assembling a separate optical die 326 (i.e. placinga combined prism/optics component directly on the spacers 322, 324).Similarly, although embodiments are depicted in which substantially alloptical elements (other than, perhaps, the objective lens andquarterwave plate) are formed in or on two units (the optical elementunit and the periscope), it is possible to implement the presentinvention using three or more units to provide the optical elements.Although in embodiments depicted herein, a polarization beam splitterwas used for discriminating emitted and reflected light, othertechniques or devices for discriminating emitted and reflected light1722 (FIG. 17) can be used including diffraction gratings, as will beunderstood by those of skill in the art after understanding the presentdisclosure. Although embodiments have been described in which aperiscope application provides two changes of direction (vertical tohorizontal and horizontal to vertical) (which can be of use in reducingthe height profile, without unduly limiting optical path length), it isalso possible to provide configurations in which multiple internalreflections between (typically parallel) surfaces (such as three ormore) are used, e.g. for reducing an optical head profile. In someembodiments it may be preferable to configure the system such that theperiscope prism (or other components of the stacked optical head) aresubstantially symmetric in configuration (e.g. to enhancemanufacturability). Although embodiments have been described in whichsubstantially all optics components of the optics head are fixed withrespect to one another, it is also possible to provide operableconfigurations in which some components are movable. For example, it ispossible to construct an operable device in which the objective lens ismovable with respect to one or more components of the optics head, e.g.for fine (or coarse) focus, tracking or the like. Although embodimentshave been described in which wafer-scale and/or stacking approaches areused, it is also possible to provide some or all optical componentsusing integrated optics techniques, as will be understood by those ofskill in the art after understanding the present invention. Although theoptics head with periscope sections and/or with substantially allcomponents being relatively non-movable has been described in connectionwith a device in which tracking is provided by rotation of an optics armabout an axis parallel to the spin axis, it is also possible toconfigure a device in which an optics head substantially as describedherein is moved in other fashions, such as providing rails or similardevices for achieving linear (e.g. radial) tracking motion of theoptical head. Although embodiments are described herein which have adiode 1712 (FIG. 17) or other laser as a light source, it is possible toprovide embodiments of the present invention which use non-laser light,such as providing a superluminescent diode 1714, an incandescent,flourescent, arc, vapor or other light source. It is possible toprovide, as the light source which is in the optical head, a lightdelivery component, such as the output 1716 of a fiber optic or otherlight conveyance device, which delivers, in or to the optical head,light generated by a laser or other light generator 1718 which may, ifdesired, be positioned remote from the optical head. Use of a fiberoptic can assist in thermal management (e.g. by permitting a laser to bemounted remote from the optical head) and/or providing for circularizinga light beam.

The present invention, in various embodiments, includes components,methods, processes, systems and/or apparatus substantially as depictedand described herein, including various embodiments, subcombinations,and subsets thereof. Those of skill in the art will understand how tomake and use the present invention after understanding the presentdisclosure. The present invention, in various embodiments, includesproviding devices and processes in the absence of items not depictedand/or described herein or in various embodiments hereof, including inthe absence of such items as may have been used in previous devices orprocesses, e.g. for improving performance, achieving ease and/orreducing cost of implementation. The present invention includes itemswhich are novel, and terminology adapted from previous and/or analogoustechnologies, for convenience in describing novel items or processes,does not necessarily retain all aspects of conventional usage of suchterminology.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the invention to the form or forms disclosed herein. Althoughthe description of the invention has included description of one or moreembodiments and certain variations and modifications, other variationsand modifications are within the scope of the invention, e.g. as may bewithin the skill and knowledge of those in the art, after understandingthe present disclosure. It is intended to obtain rights which includealternative embodiments to the extent permitted, including alternate,interchangeable and/or equivalent structures, functions, ranges or stepsto those claimed, whether or not such alternate, interchangeable and/orequivalent structures, functions, ranges or steps are disclosed herein,and without intending to publicly dedicate any patentable subjectmatter.

1. A method for providing an optical head in a read/write devicecomprising: positioning a light source with respect to an optical headsubstrate; positioning at least a first optical element along an opticalpath from said light source to an objective, said optical path definesat least a farthest virtual source point; and providing at least a firstbeamshaper in said optical path wherein a farthest virtual source pointof said optical pat after said first beamshaper is provided issubstantially the same as said farthest virtual source point before saidfirst beamshaper is provided, and wherein the beamshaper changes anellipticity of a light beam transmitted by the light source along theoptical path.
 2. A method as claimed in claim 1 wherein said beamshaperand said first optical element are positioned on a single integraloptical element unit.
 3. A method, as claimed in claim 1 wherein saidfirst optical element is a non-beamshaper element.
 4. Optical headapparatus for use in a read/write device comprising: an optical headsubstrate; a light source positioned with respect to said optical headsubstrate; a first optical element positioned along an optical path fromsaid light source to an objective; and a beamshaper in said opticalpath, wherein a farthest virtual source point of said optical path aftersaid beamshaper is positioned in the optical path is substantially thesame as said farthest virtual source point before said beamshaper ispositioned in the optical path, and wherein the beamshaper changes anellipticity of a light beam transmitted by the light source along theoptical path.
 5. Apparatus as claimed in claim 4 wherein said beamshaperand said first optical element are positioned on a single integraloptical element unit.
 6. Apparatus, as claimed in claim 4 wherein saidfirst optical element is a non-beamshaper element.